1. Field of the Invention
The present invention relates to a negative electrode active material, a negative electrode, and a lithium secondary battery having the same.
2. Description of the Related Art
Lithium metal has been used as negative electrode active materials. However, because of potential dangers of short circuits and explosion due to the formation of dendrites associated with the use of lithium metals, carbon materials are more commonly used as the negative electrode active material.
The carbon materials used in negative electrode active materials for lithium batteries typically include crystalline carbon, such as graphite and artificial graphite, and amorphous carbon, such as soft carbon and hard carbon.
The amorphous carbon has high capacity, but it also high irreversibility during the charge-discharge cycle. Similarly, the crystalline carbon, such as graphite, has high theoretical capacity (i.e. 372 mAh/g), but it still has problems with short life-span.
In addition, neither the graphite nor carbon active materials can be used as negative electrodes since their current theoretical capacity (approximately 380 mAh/g) is not sufficiently high enough to be used in high capacity lithium batteries.
To address to these problems, metal composite negative electrode active materials, such as aluminum (Al), germanium (Ge), silicon (Si), tin (Sn), zinc (Zn) and lead (Pb), are being studied as alternative materials for use in lithium batteries.
However, inorganic or metal particles such as Si or Sn, which are included in the negative electrode active material, can cause volume expansion by as much as 300 to 400% when the particles are exposed to the intercalation of lithium ions.
As lithium ions are deintercalated during the discharging cycle, the inorganic particles contract thereby causing the negative electrode active material to degrade. The problem is further exacerbated by the repeated charge-discharge cycles.
Even further, the inorganic particles may become detached when the negative electrode active materials degrade, which can cause side reactions with the electrolyte to occur and reduce the battery's cycle and high rate discharge characteristics.